KR100559757B1 - CDMA Power control for paging and initial traffic channel power - Google Patents

Abstract

Code-division multiple access power control for paging channel power and initial traffic channel power may be achieved by pilot signal strength and sectors of a pilot signal as received at a desired mobile station. The optimal initial channel power is dynamically determined according to the current forward link loading of the sector. The optimal initial paging channel power and initial traffic channel power may be determined at either the base station or mobile switching center of the mobile communication system. The paging signal or call is transmitted from the base station to the mobile station via the paging channel and traffic channel at the optimal paging channel and initial traffic channel power.

Base station, paging, traffic, switching center, mobile station

Description

CDMA Power control for paging and initial traffic channel power             

1 illustrates a mobile communication system of a preferred embodiment of the present application.

FIG. 2 shows the base station 30 of FIG. 1 in more detail.

3 shows the message exchange center 40 of FIG. 1 in more detail.

Explanation of symbols on the main parts of the drawings

10: mobile station 30: base station

40: mobile switching center 50: public switched telephone network

301: antenna 303: transceiver

403: controller 405: memory

Technical field
The present invention relates to CDMA power control that dynamically determines optimal paging and initial traffic channel power to reduce call origination failure in a mobile communication system.

Description of Background Technology
Conventional CDMA when a mobile station fails to receive a BS acknowledgment signal, a channel assignment message (CAM), a forward acknowledgment (FW) signal, or a service connecting (SC) message (code division multiple access) Call initiation failures typically occur in mobile communication systems. Table 1 lists the failure rates of each of the above call initiation failures. BS approval failure (34.3% failure rate) is the main reason for call initiation failure. BS grant failures occur when the mobile station sends an access probe to the base station to request a connection from the mobile communication system, and when the paging channel power from the base station to the mobile station is insufficient and no grant is received at the base station.

No BS ACK No CAM No FW ACK NO SC Etc % Failure 34.38 9.38 31.25 20.31 4.69

IS-95-B is a mobile station-base station compatibility standard for dual-mode wide band spread spectrum. If the mobile station lost the paging channel, access probe handoff is an IS-95-B scheme to improve call initiation failure by performing a handoff on another paging channel. However, access probe handoff cannot basically resolve base station admission failures. For example, an access probe handoff only determines which paging channel to exchange, and therefore does not adjust paging channel power. When the forward link power of the paging channels is insufficient, the access probe handoff fails.

In general, base station admission failure can be reduced by increasing paging channel power. Currently, the average digital gain unit (DGU) for the traffic channel is in the range of 67-75, and the constant DGU set for the paging channel is 64. Table 2 shows the call initiation failure rates derived from field test results for the baseline case with paging channel DGU = 64, initial traffic channel DGU = 80, T50m = 0.2 seconds, and T51m = 1.0 second. Enumerate. In this example, a time limit of T51m = 1.0 second is set for the mobile station to report the reception of two good traffic channel trames sent from the base station to the base station. After the first good traffic channel frame, the second good traffic channel frame must be received within a time limit of T50m = 0.2 seconds. After the mobile tunes to a particular traffic channel, the call is dropped if no acknowledgment reports of two good traffic channel frames are sent to the base station within T51m = 1.0 seconds. In the case of the baseline, 13.03% of all calls are failed and 4.48% of all calls fail due to base station admission failure, which is 34.38% of all failed calls.

Occation Actual failure rate No BS ACK% No CAM% No FW ACK% NO SC% Etc% 0 Baseline 13.03 (100) 4.48 (34.38) 1.22 (9.38) 4.07 (31.25)  2.65 (20.31) 0.61 (4.69) One PG DGU = 90 Traffic DGU = 108 13.38 (100) 2.12 (15.87) 1.06 (7.94) 7.86 (58.73) 1.70 (12.70) 0.64 (4.76) 2 T50m = 1 sec T51m = 2.8sec 10.14 (100) 3.86 (38.10) 0.97 (9.52) 0.72 (7.14) 2.66 (26.19) 1.93 (19.05) 3 PG DGU-90 Traffic DGU = 108 T50m = 1sec T51m = 2.8sec 7.26 (100) 1.21 (16.67) 0.4 (5.56) 2.42 (33.33) 3.02 (41.67) 0.02 (2.78)

Compared to the baseline case, as can be seen in Case 1, the test results in Table 2 show that the increased paging channel DGU improved the base station admission failure rate by 50% or more. However, increased paging channel power can negatively impact mobile communication system capacity in terms of system power budget. Since more power is allocated to the paging channel, less power is available for the traffic channel. In addition, system noise increases as paging channel power increases, which contributes to increased interference. As can be seen further in Case 1, the increased paging channel power reduces the base station admission failure rate, but the forward signal admission failure rate increases significantly due to the increased interference. This results in a reduction of about 2.5 forward link users. To mitigate this negative impact, the T50m and T51m time restrictions can be increased as in Case 2, so that base station admission failure rate can be improved. However, this approach is not practical because mobile units must be serviced to change T50m and T51m time limits.

Summary of the Invention
In the present invention, the paging channel power and initial traffic channel power are determined according to the current RF conditions and are dynamically set so that when the RF conditions are bad, the channel power can be increased and when the RF conditions are good, the channel power is Can be reduced. The present invention determines the optimal paging channel power and initial traffic channel power according to the current forward link loading of the base station and the pilot signal strength of the pilot signal received at the mobile station. The base station then sends a paging message or call to the mobile station over the traffic channel and the paging channel at the determined optimal initial traffic channel power and the determined optimal paging channel power.

Detailed Description of the Preferred Embodiments
1 illustrates a CDMA mobile communication system of a preferred embodiment of the present application. As illustrated in FIG. 1, the mobile communication system includes a number of base stations 30, 31, and 32 that transmit and receive communication signals to / from the mobile station 10. Although not shown, each base station can cover each sector. The mobile switching center 40 is coupled to a number of base stations 30-32 via communication lines L and also enables communication between the mobile station 10 and a public switched telephone network (PSTN) 50. To a public switched telephone network (PSTN). Although each of the three base stations is illustrated, it will be understood that the mobile communication system may include any number of base stations.

2 shows base station 30 in more detail. Transceiver 303 transmits and receives RF signals to / from mobile station 10 via antenna 301. The transceiver 303 and antenna 301 may be any conventional transceiver and antenna and may operate in a conventional dual communication mode that enables the transmission and reception of RF signals. Alternatively, the transceiver 303 may be replaced with a separate transmitter and receiver pair, and the antenna 301 may include a transmit antenna and a receive antenna. The transceiver 303 demodulates and filters the RF signals received from the mobile station 10 via the antenna 301, and provides a corresponding demodulated received signal to the controller 305. The transceiver 303 also modulates and amplifies the transmission signal provided from the controller 305 and provides the modulated transmission signal to the antenna 301 for transmission to the mobile station 10 as an RF signal.

The base station 30 further includes a transceiver 309 that transmits and receives signals to / from the mobile switching center 40 via communication lines L. The transceiver 309 may be any conventional transceiver known to those skilled in the art. In an alternative embodiment, the transceiver 309 may include a transmitter and receiver pair for transmitting and receiving signals to / from the message exchange center 40 via the pair of communication lines L.

The operation of the base station 30 is controlled by the controller 305 in the manner described below. The controller 305 may be a microprocessor that controls the operation of the base station 30 in accordance with software programming stored in the memory 307. As will be readily appreciated by those skilled in the art, the controller 305 may alternatively include various discrete hardware circuit elements and is not necessarily limited to being based on a microprocessor. In addition, to store operating programs for the base station 30, the memory 307 includes a working memory that can be used by the controller 305.

3 illustrates the mobile switching center 40 in more detail. Transceiver 401 is coupled to communication lines L to receive and transmit signals from / to base stations 30-32. The transceiver 401 may be any conventional transceiver available at a mobile switching center as will be appreciated by those skilled in the art. In an alternative embodiment, the transceiver 401 may include a transmitter and receiver pair that transmits and receives signals individually over a pair of communication lines (L). The operation of the mobile switching center 40 is controlled by the controller 403 as described in more detail below. The controller 403 may be based on a microprocessor and operate to control the operation of the mobile switching center 40 in accordance with software programming stored in the memory 405. The memory 405 may also include a working memory area usable by the controller 403. The controller 403 is also coupled to the PSTN 50.

The operation of the preferred embodiment of the present application will be described with reference to Figs. 1-3. The following notation will be used throughout the description. Ec / Io is the pilot signal strength or pilot power of the pilot signal received at the mobile station. L_F is the current forward link loading of the base station in the desired sector. The current forward link loading is derived as the ratio of the base station's current transmit power to the base station's maximum transmit power. L_F is reported by the base station and may be determined by the controller 305 of the base station 30 based on the Ec / Io of the pilot signal. Typically, the maximum transmit power of the base station is 8 watts. T_pilot is the pilot power transmitted from the base station of the desired sector and is generally set to 15-20% of the maximum transmit power of the base station. F_pilot is the ratio of transmitted pilot power to maximum transmitted power of the base station, typically 15%. P_pilot is the received pilot power at the mobile station. (Eb / No) p is the required quality of the paging channel or, in other words, the required bit energy level of the paging channel. (Eb / No) t is the required quality of the traffic channel or, in other words, the required bit energy level of the traffic channel. In general, (Eb / No) p and (Eb / No) t are set to 7 dB, but if desired, may be set to approximately 9 dB. It is to be understood that the values given above are examples and may be set as desired and therefore should not be considered limiting.

In the preferred embodiment, the mobile station 10 of FIG. 1 first locks to the strongest pilot signal and generates a pilot measurement message (PSMM) confirming the received pilot signal and pilot signal strength (Ec / Io). Let's do it. For example, when locking with a pilot signal from the base station 30, the mobile station 10 transmits a PSMM to the base station 30. The controller 305 of the base station 30 then determines the optimal paging channel power and initial traffic channel power according to the software programming stored in the memory 307 based on the reported pilot signal strength and the current forward link loading. Interference ratios of internal interferences generated within the desired sector or cell and external interferences created by other cells plus noise, known or easily derived required qualities (Eb / No) p and (Eb / No) t, an assumed orthogonal factor (O) is used to determine the optimal paging channel power and initial traffic channel power at a specific time as follows.

 Specifically, the pilot signal strength reported by the mobile station can be expressed as follows:

Here, I_in and I_out are internal interference and external interference, respectively, and include thermal noise. The inverse of the pilot signal strength can be expressed as follows:

Since the pilot power is a fixed percentage of the total maximum output power of the base station 30, the ratio of internal interference to received pilot power at the mobile station 10 can be expressed as:

Substituting Equation 3 into Equation 2 is as follows:

From Equation 4, since I_out = P_pilot x A, the ratio of external interference to internal interference of other cell plus noise can be expressed as:

The required received paging channel power p_page may be expressed as a target quality (Eb / No) p as follows:

Where O is an orthogonal factor for internal interference. Since Walsh codes are used in a CDMA mobile communication system, the channels of the respective sectors are orthogonal and thus do not interfere with each other during demodulation. However, multipath signals from a single source exist in a CDMA mobile communication system. Although the multipath signal is transmitted simultaneously, it may not be received by the mobile station at the same time due to the time delays caused by the reflections from the objects. Thus, the corresponding received channel may not be exactly orthogonal, thus increasing internal interference. Orthogonal elements provide a measure of internal interference due to multipath. Typically, the orthogonal element can be set to 0.1 or 0.2.

Equations 6 and 7 represent the required quality (Eb / No) p of the paging channel and the received paging channel power P_page required for internal and external interference. The ratio of the received paging channel power (p_page) required for internal interference (I_in) occurring within the sector is the current transmission occurring within the sector because the propagation loss between the base station and the mobile station is equal at a given instant. Equal to the ratio of the requested transmit paging channel power T_page to the received power T_in.

Therefore, the required transmission paging channel power T_page can be solved by substituting Equation 6 into Equation 7,

From Equation 5, I_out can be expressed as follows:

Substituting Equation 9 into Equation 8 gives:

If you rearrange it,

T_in can be expressed as:

Substituting Equation 11 into Equation 12, T_page, which is a required transmission paging channel power or an optimal initial paging channel power, can be finally expressed as follows:

Since all values of Equation 13 are determined or known once the pilot signal strength of the pilot signal is reported by the mobile station, the required transmit paging channel power for the corresponding RF and forwarding loading states is determined by the controller 305. Can be determined. The controller 305 then controls the transceiver 303 to transmit the corresponding paging message via the paging channel to the mobile station 10 via the antenna 301 at the required transmit paging channel power. Since the optimal paging channel power is dynamically determined according to current RF conditions, the paging channel power can only be increased to the extent necessary when needed. Similarly, paging channel power may be reduced when RF conditions are allowed. Thus, the system power budget is effectively allocated and the interference generated is minimized.

In a more preferred embodiment, the optimal paging channel power may be determined by the controller 403 of the mobile switching center 40 according to the software stored in the memory 405. In this embodiment, the PSMM is generated by the mobile station 10 and transmitted to the base station 30. Base station 30 then sends PSMM to mobile switching center 40 via lines L. Thereafter, the controller 403 transmits to the base station 30 based on the PSMM and the current forward link loading of the base station 30 determined based on the pilot signal strength reported according to Equation 13 as described in the first embodiment. Determine the required transmit paging channel power for The controller 403 then instructs the transceiver 401 to send information indicating the required transmitted paging channel power to the base station 30, which then sends a paging message over the paging channel with the requested transmission paging channel power. To 10. An advantage of this embodiment is that the paging channel power can be controlled and set by the mobile switching center 40 without base station software and resources.

In another embodiment, the optimal initial traffic channel power may be determined according to the pilot signal strength reported from the mobile station as follows.

(14) except that the required quality (Eb / No) t of the traffic channel is used in Equation 14 instead of the required quality of the paging channel (Eb / No) p of Equation 13. Is the same as According to the first and second embodiments, the required traffic channel power may be determined at the base station 30 or at the mobile switching center 40.

Programming required to execute the processes described in accordance with the embodiments described above is not limited to being stored in the memories 307 and 405 of the base station 30 and mobile switching center 40 of FIGS. 2 and 3, respectively. Will be understood. The programming may be recorded on a computer readable medium, such as a floppy disk or a CD ROM, readable by the controllers 305 and 403 of the base station 30 and the mobile switching center 40, respectively. Alternatively, programming may be sent from the mobile switching center 40 to the controller 305 of the base station 30 via a signal pre-populated along the line L.

It will also be understood that power control for paging channel power and initial traffic channel power is not necessarily limited to the corresponding figures, description example values. For example, the values of the maximum transmit power, T_pilot, F_pilot, (Ec / No) t, (Ec / No) p and orthogonal element O may be preset by the service provider and the memories 307 and 405 ) Can be stored. Further, although the controller 305 of the base station 30 and the controller 403 of the mobile switching center 40 are described as being based on a microprocessor operating according to software programming stored in the memories 307 and 305, respectively, the controller 405 and 403 may be discrete circuit elements including multipliers and adders or logic gate arrays. Also, the controllers 305 and 403 may be integrated memory where the memories 307 and 405 of FIGS. 2 and 3 are not necessarily required. Further, as described, initial paging channel control and power control of initial traffic channel power are not necessarily limited to CDMA systems and can be applied to any mobile communication system as will be appreciated.

The present invention relates to CDMA power control for dynamically determining optimal paging and initial traffic channel power to reduce call initiation failures in a mobile communication system.

Claims (26)

In the base station of the mobile communication system, A transmitter for wirelessly transmitting a pilot signal and a paging message to a mobile station of the mobile communication system; And A controller for determining an optimum paging channel power according to pilot signal strength of the pilot signal wirelessly received by the mobile station and forward loading of the base station; Wherein the transmitter wirelessly transmits the paging message to the mobile station over a paging channel at the optimal paging channel power. The method of claim 1, Wherein the forward loading of the base station is a ratio of the current transmit power of the base station to the maximum transmit power of the base station. The method of claim 1, The controller also determines an optimal initial traffic channel power according to the pilot signal strength. delete In the mobile switching center of the mobile communication system, The mobile switching center is supplied with an indication indicating pilot signal strength of a pilot signal wirelessly received by a mobile station of the mobile communication system, The mobile exchange center is: And a controller for determining an optimal paging channel power for wireless transmission of a paging message to the mobile station, in accordance with pilot signal strength of the pilot signal and forward loading of a base station. The method of claim 5, The controller supplies information indicative of the optimal paging channel power to a base station of the mobile communication system, and the paging message is wirelessly transmitted from the base station to the mobile station at the optimal paging channel power. Exchange center. The method of claim 6, Forward loading of the base station is a ratio of the current transmit power of the base station to the maximum transmit power of the base station. The method of claim 5, The controller also determines an optimal initial traffic channel power in accordance with the pilot signal strength. delete In the method for controlling the transmission power of the base station of the mobile communication system, Wirelessly transmitting a pilot signal to a mobile station of the mobile communication system; Determining an optimal paging channel power according to pilot signal strength of the pilot signal wirelessly received by the mobile station and forward loading of the base station; And Transmitting wirelessly a paging message to the mobile station over a paging channel at the optimum paging channel power. The method of claim 10, Forward loading of the base station is a ratio of the current transmit power of the base station to the maximum transmit power of the base station. delete delete The method of claim 10, Determining an optimal initial traffic channel power according to the pilot signal strength; And And wirelessly sending a call to the mobile station over a traffic channel at the optimum initial traffic channel power. delete delete delete delete delete delete delete delete delete delete delete delete

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